1. Field of the Invention
The invention disclosed herein relates to electrophotography and electroradiography and in particular to a system and method for creating an electrical charge pattern in accordance with a radiation image pattern on the insulative layer of an integral sandwich structure including an insulative layer-photoconductive layer-conductive layer.
2. Prior Art
Prior approaches to the creation of an electrical charge pattern in accordance with a radiation-image pattern on the insulative layer of an integral sandwich structure including an insulative layer-photoconductive layer-conductive layer have involved the use of corona discharge devices as a charge source and in some cases more than one type of corona discharge devices. A radiation image pattern is used during a period of operation of the corona discharge device. Such prior approaches are described in two articles appearing in IEE Transactions on Electron Devices, Vol. ED-19, No. 4, April 1972. The first article is found at page 396 and the second article at page 405.
Such prior approaches to the creation of an electrical charge pattern on the insulative layer of insulative layer-photoconductive layer-conductive electrode structure do not provide for large area exposure if high quality gray scale reproduction is to be obtained. Such results require a charge source which must be capable of supplying a very uniform charge density proportional to the incident radiation.
Corona discharge devices are subject to geometric and wire surface irregularities and, therefore, do not lend themselves to large area charging without scanning and in addition the charge delivery rate of corona discharge devices is subject to variation due to environmental conditions, and is limited by corona design constraints.
The application of an electrical charge by placing a removable conductive surface in close proximity to the insulative layer while a voltage is applied to it with respect to the conductive layer is not acceptable due to variations in the air gap presented.